Although no liferaft
on my boat (and not on my wishlist at the moment) - I have humped around a few liferafts over the years.
For me a Valise would win, and accepting that there may be issues on rapid deployment (from bottom of a locker!) and losing some stowage space, but that outweighed by easier handling to the best launching spot. (a cannister liferaft, especially 6 man plus is a heavy bugger, and when wet can be like wrestling a greased pig!).
Throw in that a Liferaft should last longer by not sitting on deck 24/7 (I know it's sealed, but still.......) and it won't be swept off the deck (leaving holes behind would be my big worry, rather than losing the liferaft - as in conditions that would do that the odds are getting into a liferaft (if you can!) won't be a long term survival event).
Having said all that, I don't think there is any slam dunk right answer either way - it's what works for you / what you are comfortable with.